The present invention relates to sheet material cutting apparatus of the type used for cutting pattern pieces from single or multi-ply layups of sheet material. More particularly, the invention relates to a sharpenable cutting blade adapted for use in such apparatus.
Sheet material cutting apparatus of the general type mentioned has been in existence for some time. A well-known and commercially accepted apparatus, illustrated and described in U.S. Pat. No. 3,955,458 to Pearl dated May 11, 1976 entitled Cutting Apparatus With Sharpener and Sharpening Method and in other patents to the same assignee, has a reciprocating cutting blade which is suspended in cantilever fashion over a support table on which the sheet material is held in a spread condition during cutting. The cutting blade is of an elongated thin, flat configuration and has a sharp forwardly facing cutting edge defined by and between a pair of acutely angularly related and intersecting surfaces. The blade is reciprocated longitudinally and advanced laterally through the sheet material along predetermined cutting paths at the periphery of pattern pieces. The blade is also adapted for rotation about its own longitudinal axis in order to remain generally tangent to the cutting path in movement therealong. Optionally, the blade may also be adapted for rotation about its longitudinal axis with the axis held in a fixed position for a sheet material drilling operation.
It is also a known practice in sheet material cutting apparatus of the type mentioned to provide for "on-line" sharpening of the cutting blade. That is, in order to minimize apparatus downtime, a blade sharpening device may be included in the apparatus to carry out a sharpening operation without removing the blade from the apparatus. Obviously, removal and replacement of blades and resulting apparatus downtime has significant detrimental effect on production rates.
U.S. Pat. No. 4,033,214 by Pearl, dated July 5, 1977 entitled BLADE SHARPENER to the present assignee illustrates and describes cutting blade sharpening devices incorporated in sheet material cutting apparatus and adapted for "on-line" sharpening. Grinding wheels are employed for sharpening in an automatically operable mechanism which moves the wheels into engagement with the aforementioned longitudinally extending edge defining surfaces on the blade whereby to remove surface material from the surfaces and to sharpen the edge. In the devices shown in the application, grinding wheel and blade engagement is effected during blade reciprocation and the aforesaid surfaces have generally uniform cross sectional contours viewed longitudinally. Thus, the longitudinally extending edge is effectively sharpened throughout its length.
Despite the foregoing, the significant advantages of "on-line" sharpening are somewhat tempered by limitations imposed on blade design. Sharpening devices of the type mentioned have limited capabilities. While they may be highly effective in sharpening a blade having a single longitudinally extending cutting edge bounded by a pair of longitudinally extending surfaces, blade designs with more complex cutting edges fall beyond their ambit. Thus, complex cutting edges which may include a main longitudinal edge and small auxiliary edges displaced from the main edge bounding surfaces cannot be effectively sharpened. Such blades, on the other hand, may be most desirable from the standpoint of cutting efficiency.
It is the general object of the present invention to provide an improved sharpenable cutting blade of the type mentioned and which includes both main and auxiliary cutting edges in a configuration which exhibits a high degree of cutting efficiency, and which is yet readily sharpenable with a sharpening means limited in its capability to engagement with main edge bounding and defining surfaces.
A further object of the present invention resides in the provision of a cutting blade of the type mentioned wherein the auxiliary cutting edges are so arranged as to be sharpened simultaneously with the main cutting edge by engagement of a sharpening means with the aforesaid main edge defining surfaces.
A still further object resides in the provision of a blade of the type mentioned wherein the auxiliary cutting edges are so oriented as to provide balanced and multi-directional cutting action.